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PDBsum entry 3dsp
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Metal binding protein
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PDB id
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3dsp
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References listed in PDB file
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Key reference
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Title
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Unprecedented binding cooperativity between cu(i) and cu(ii) in the copper resistance protein copk from cupriavidus metallidurans ch34: implications from structural studies by nmr spectroscopy and X-Ray crystallography.
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Authors
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L.X.Chong,
M.R.Ash,
M.J.Maher,
M.G.Hinds,
Z.Xiao,
A.G.Wedd.
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Ref.
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J Am Chem Soc, 2009,
131,
3549-3564.
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PubMed id
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Abstract
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The bacterium Cupriavidus metallidurans CH34 is resistant to high environmental
concentrations of many metal ions, including copper. This ability arises
primarily from the presence of a large plasmid pMOL30 which includes a cluster
of 19 cop genes that respond to copper. One of the protein products CopK is
induced at high levels and is expressed to the periplasm as a small soluble
protein (8.3 kDa). Apo-CopK associates in solution to form a dimer (K(D)
approximately 10(-5) M) whose structure was defined by NMR and X-ray
crystallography. The individual molecules feature two antiparallel beta-sheets
arranged in a sandwich-like structure and interact through C-terminal
beta-strands. It binds Cu(II) with low affinity (K(D)(Cu(II)) > 10(-6) M) but
Cu(I) with high affinity (K(D)(Cu(I)) = 2 x 10(-11) M). Cu(I)-CopK was also a
dimer in the solid state and featured a distorted tetrahedral site
Cu(I)(S-Met)(3)(NCS). The isothiocyanato ligand originated from the
crystallization solution. Binding of Cu(I) or Ag(I), but not of Cu(II), favored
the monomeric form in solution. While Ag(I)-CopK was stable as isolated,
Cu(I)-CopK was moderately air-sensitive due to a strong binding cooperativity
between Cu(I) and Cu(II). This was documented by determination of the Cu(I) and
Cu(II) binding affinities in the presence of the other ion: K(D)(Cu(I)) = 2 x
10(-13) M and K(D)(Cu(II)) = 3 x 10(-12) M, that is, binding of Cu(II) increased
the affinity for Cu(I) by a factor of approximately 10(2) and binding of Cu(I)
increased the affinity for Cu(II) by a factor of at least 10(6). Stable forms of
both Cu(I)Cu(II)-CopK and Ag(I)Cu(II)-CopK were isolated readily. Consistent
with this unprecedented copper binding chemistry, NMR spectroscopy detected
three distinct forms: apo-CopK, Cu(I)-CopK and Cu(I)Cu(II)-CopK that do not
exchange on the NMR time scale. This information provides a valuable guide to
the role of CopK in copper resistance.
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